Photomechanical process



March 1946- A. MURRAY ETAL PHOTOMECBANIGAL PROCESS Original Fil ed April5, 1940 4% F76. v -/0 /z FILTER /5 V Lg /7 FLUORESCENT 3L LIGHT ONLYORIGINAL (FLUORESCENT P/GMENTJ) VISUAL HL/E 0F PAINT PROPORT/O/YS 0FFLUORESCENT ALEXA/YDERMz/RRAY JOHN/4.6. YuLE INVENTORS I BY al PR/MARGREEN ATTORNEY Reissued Mar. 26, 1946 PHOTOMECHANICAL PROCESS AlexanderMurray and John A. C. Yule, Rochester, N.'Y., assignors to Eastman KodakCompany, Rochester, N. Y., a corporation of New Jersey OriginalNo.2,278,114, dated March 31, 1942, Se-

rial No. 328,066, April 5, 1940. Application for reissue November 8,1945, Serial No. 627,504

4 Claims.

This invention relates to photomechanical processes and particularly toprocesses for the reproduction of colors.

It is an object 01' the invention to provide a method and means formaking color separation records which require little or no retouching inorder to reproduce colors accurately.

It is also an object of the invention to provide such a method of makingcolor separation records which will not require any step of colorcorrection such as masking.

It is an object of the present invention to pr vide a method of makingcolor separation positives directly from a colored original.

It is a particular object of the invention to provide a palette ofartists paints with which a picture can be painted, which picture willhave the natural appearance desired and still can be reproduced directlywithout retouching.

It is an object of a special embodiment of the invention to provide apalette 01 artists paints particularly-adapted to be reproduced by aphotomechanical process employing a black printer and a method ofemploying this palette of paints.

' According to the present invention, an original. paintingto bereproduced photomechanically is created by the artist with inks, dyes,or paints, containing three fluorescent ingredients. For simplificationthe word paint will be used to cover all artists coloring materials.These ingredients are such that their fluorescent hues are mutuallyseparable spectrally. That is, they are of such fluorescent color (e. g.violet, green, and red) that their spectral distribution of intensitycurves do not overlap or if they do overlap, it is only partial andthere is in each of the three hues one wave-length portion which is notin the other support for the original should contain no fluorescentingredients. A black ink (or other black paint) must contain all threeingredients except in one special embodiment described later wherein itcontains no fluorescent ingredients.

The other factors which determine the amounts of fluorescent ingredientsin any one material are the fluorescent efliciency of the ingredient ineach material and the amount of ingredient used in the other materials.Certain pigments absorb ultra violet and/or the fluorescent wavelengthsthemselves more than other pigments do. Thus a red pigment, say, mayrequire ten times as much fluorescent ingredient as a yellow pigment inorder to give the same effect. Thus the ingredients are effectively butnot actually in proportion to the subtractive color contents of two. Ineither case, any one of the hues can be 1 selected by a suitable colorfilter which absorbs the other two hues completely.

In simple theory the relative amounts of the three ingredients in eachpaint are proportional to the subtractive color contents of the hue orthat paint. Actually they are also proportional to other factors to bediscussed below. Roughly, the subtractive color contents are the amountsof yellow, magenta, and blue-green making up the hue; more exactly theyare the amounts 0! minus blue, minus green, and minus red. We

,speak of primary color components" (white is made up of all threeprimary colors) and of subtractive color contents (white has nosubtractivecolor contents). For example, a yellow paint must" tain onlyone of these fluorescent in gredi a white paint it used and the whitethe materials. Furthermore the proportionality needs to be satisfiedonly for "each of the three ingredients separately, not relative to oneanother because in the process, exposures are made separately to eachfluorescent hue and need not be equal. For example in one particularset-up we have used, we expose 10 seconds for one hue and 5 minutes foranother. 1

Positive color separations are made for this original by photographingit successively on three. diiierentphotosensitive layers usingfluorescent light only and in each case using only one of thefluorescent hues. This is accomplished by illuminating the original withfiuoroactivating light such as ultra-violet (all visible light havingbeen filtered out) and then by using suitable filters allowing one onlyof the fluorescent hues to reach the sensitive film in each case.

Ifa black printer is to be used, it may be prepared byany of the usualmethods, but we prefer to use the method described by one of us in U. S.2,161,378, Murray, since it combines uniquely with a specialmodification or the present invention;

The result has the advantage that none of the color printers print whereonly the black printer need print, i. e. where the original picture ismade up entirely of a black pigment. v

To meet the requirements of U. S. 2,161,378,

this special embodiment of the present invention employs coloringmaterials for creating the original which with exception of the black,reflect or transmit infra-red freely (i. e. do not absorb it). The blackpigment used absorbs infrared and an infrared separation negative makesa black printer which is a practically perfect one of the type whichreproduces only those blacks and grays in the original which are made ofthe black pigment used in creating the original. To conlight indicatedby arrows I! which fluorescent light;

form with the present invention in its simplest form, this black pigmentwould contain all three fluorescent ingredients since it includes allthree subtractive colors. However, to gain the advantage of this specialembodiment wherein no color printers will print where there is onlyblack in the original, this black pigment is made up with no fluorescentingredient, the same as white is. v Thus this special embodiment of theinvention employsa palette of coloring materials for creating theoriginal, which palette includes a black paint which contains nofluorescent ingredient and a plurality oi. other paints or inks whichcontain three fluorescent ingredients in respective proportion to thesubtractive color contents of the hues of these other coloringmaterials, (flu.- orescent emciency being taken into account as before).The color separation positives are then made in the same way as whenintended for a three-color process and the black positive is made froman infrared separation negative.

other objects and advantages of the invention will be apparentfrom thefollowing description when read in connection with the accompanyingdrawing in which:

Fig. 1 illustrates one embodiment tion. 1

Fig. 2 illustrates the optical properties of the artists color materialsemployed by the present invention.

Fig. 3 is included merely toasslst in explaining the principlesunderlying the invention.

In Fig. 1 an original painting in including'flucrescent pigments isilluminated by sources H 01' illumination which send outfluoro-activating causes the original III to fluoresce. The lightsources H are such (tor example an ultra-violet arc with a 111- ter toabsorb the visible light) that none of the light [2 (before or afterdirect reflection by the of the invenorange, etc. He may also employ awhite and/or a black paint or ink. According to the invention each ofthese paints includes a fluorescent ingredient, the relative eflectiveamounts oi the ingredients in any one paint being in proportion to thesubtractive color contents of that paint. As pointed out, the actualamounts depend on the absorption 01' the fluorescent light and of thefluoro-activating light by the paint and-on the amounts used in theother paints. For example. a magenta paint'which contains no yellow orblue-green content would include only one of the ingredients, namely,that whose fluorescent hue is labeled hue I" in circle Zll. Similarlyyellow would include only the ingredient having hue II" and blue-greenwould include only the ingredient having hue III. A primary red paint onthe other hand would include effectively equal amounts of theingredients having hues I and II." In this example, if the primary red'paint absorbs ultra-violet and light of hue I much more than the magentapaint, one would require more of hue I ingredient in the primary redpaint than hall of that in the magenta paint. The onehalf value ispredicted from simple theory. Also the actual proportion of the hue Iingredient to the hue II ingredient in the primary red paint depends onthe relative efliciency of these ingredients and the exposures to begiven for each hue. The amount of fluorescent ingredient in theblue-green paint 2| is illustrated by the block 22. The correspondingblocks for the magenta and yellow are thesame size to indicate that withthe differences in exposure taken into account,

original In) is of the same wavelength as the V The light coming iromthe original Ill indicated by arrows II is made up of fluorescent lightand reflected light. A fllter II is placed in the path of this lightfrom the original to absorb all wave lengths included in the light I2and to transmit only fluorescent light I5. Of course the fllter Il mayabsorb some of the fluorescent light of the hue to be transmitted andalways absorbs any fluorescen light of other hues. By means oi. a lensli, a photosensitive layer I1 is in printing relation to the original inand is exposed by the fluorescent light I5.

According to the present invention, the original I II is made up ofpigments containing three fluorescent ingredients having different hueswhich are mutually separable spectrally. Therefore, the light It mayinclude fluorescent light from all three fluorescent pigments and byproper selection of fllter ll. the process illustrateffectively equalamounts of the ingredients must be used. The amount of fluorescentingredients in primary green 23 is illustrated by equal blocks 24, but01' course this means that the relative amounts of the two ingredientsin primary green must be such that their fluorescent intensities areeffectively equal, when measured with respect to the spectralsensitivity of the photographic films to be used and the exposures to begiven. Any intermediate color such. as orange indicated by the brokenline 25 would have relative amounts of the fluorescent ingredientsindicated by the blocks 26 and 21 corresponding to the subtractive colorcontents of this hue-orange.

Since orange is made up mainly of yellow with a small amount of magentathe block 26 is larger than the block 21.

Another way of looking at this phase of the matter, which is a littlecomplicated because of is, of course, directly in terms of thesubtractive color contents, (applying the term to areas of the originalin this case). This simplifies the mathematicsbecause only the threecolors are present. From this latter point of view, any areas on theoriginal Ill requiring for their reproduction equal amounts ofblue-green ink should have eflectively equal amounts of the hue IIIingredient. That is, any blue, blue-green, orgreen areas whosebrightnesses are such that they are equivalent in blue-green, requireequal amounts of blue-green in their reproduction and hence shouldcontain effectively equal amounts of hue III ingredient. A green areamade of superimposing blue-green and yellow coloring materials willcontain equal (effectively) amounts of the corresponding ingredients andwilloi course-contain just as much hue. III ingredient as when theyellow is omitted and only blue-green is used. However, when all of thisis transferred from a discussion of areas to one of coloring materialson a palette, a green paint contains only half as much (eifectivcly) ofingredient hue III" as does a blue-green paint. The point is that over aunit area there is twice as much paint when the yellow is added as whenthe blue-green is alone so that the proportion of hue III ingredient tototal paint is halved althoughthe proportion to area is unchanged.

The actual fluorescent hues of the fluorescent ingredients areimmaterial. For example hue I may be violet, hue 11 may be green and hueIII may be red. As long as the fluorescent hues are mutually separablespectrally, it does not matter in what order they appear in circle 20.

'By selecting the proper amounts of fluorescent ingredients in each ofthe paints, all or most retouching is eliminated from subsequentprocesses. The difliculty in compounding a paint which has exactly thecorrect fluorescence throughout all of its range of tints may in somecases result in slightly excessive brightness of the pastel shades, butany retouching required is considerably less than that formerly used andfor most purposes for which we have used this process, no retouching hasbeen necessary. The amount of fluorescent ingredient indicated by theblock 22 in the blue-green paint 2| should be effectively proportionalto the density required in a blue-green separation positive forming-thebluegreen printer. Similarly, the amounts of the ingredients representedby the blocks 24 should correspond to the required printer densities tobe used with the yellow and blue-green inks in the final process toreproduce primary green as it appears in the original. That is, theblocks 22, 24, 26, and 21 are representative of the effective amounts offluorescent ingredients required in terms of final printer densitiesrequired.

From Fig. 2, it is obvious that the present invention must result inpositives directly. When using ordinary non-fluorescent pigments, themore of the pigment present at any point the greater is the opticaldensity of that point. In

ing hue II. The fluorescent hue circle is rotated 60 degrees relative tothe circle 20* of Fig. 2. Color separation records made using thefluorescent hues only from such an arrangement would be dense where thecolors are densest and hence positive in density. However, (leaving outthe theoretical possibility of shifting to new primaries and havingsubtractive inks with hues corresponding to ordinary primary colorswhich cent hues in the circle ZO-so that the visual hues of thefluorescent ingredients (not their fluorescent hues which are labeled I,II, and III) correspond most nearly to the visual hues of the paints inwhich they are to be used. It is also desirable that the fluorescentingredients be chemically stable and stable to light and to exposure tothe atmosphere. For aqueous paints the fluorescent ingredients arepreferably nonvolatile, water insoluble, pulverable materials ofrelatively low optical density in their own visual color, but of highdensity to ultra-violet to increase fluorescence efiiciency. Thefollowing fluorescent materials are satisfactory when used with mercuryvapor lamps as a source of fluoroactivating light: chrysene, anthracenewith a trace of naphthacene (or chrysene with 1% naphthacene) andrhodamine G precipitated with a water insoluble gum or resin.

the present case however, a large amountof pigment corresponds to alarge amount of fluorescent material and hence to increased brightness.Thus the film ll when processed has a high density (due to highbrightness of fluorescence) wherever the original has a high density ofpigment. Thus the result is a positive.

In this general connection, Fig. 3 illustrates why the present inventionis restricted tothe making of positives directly, which is of course oneof its added advantages. It is customary in ordinary three-color work tophotograph the original through primary filters red, green, and blue togive negatives. If one were to attempt to modify the present inventionto give negative in the same way and arranged so that the I pigmentswere made up with fluorescent ingredients added in proportion to theprimary color components as illustrated in Fig. 3, the resultant recordswould be negative as far as colors, are

concerned, but they would be positive as far as density is concerned.That is, the records would be white where the original was white andwould be black where the original is black. A subtractive color, forexample blue-green, as shown by 3| would be made up of equal portions 32of fluorescent hues II and III. Similarly a primary color such asprimary green shown by 33 would as shown by block 34 contain only one ofthe fluorescent ingredients, namely that hav- Chrysene when illuminatedwith light of 365 millimicron wave length through a filter (such as Corning Glass Co. #584) absorbing the visible spectrum fluoresces with aviolet light of about 400 to 450 millimicrons. A filter (such as a com-.bination of Wratten #34 and Wratten #2A) transmitting only this latterWave length band or part of it, may be used over a camera by which acolor separation positive is to be made.

' Since this latter filter combination transmits red,

be added to the combination.

only orthoor blue-sensitive emulsions should be used therewith or ared-absorbing filter should Pure anthracene plus 1 per cent naphthalenewhen excited by ultra-violet light of the same wave length (365)fluoresces in the green region from about 500 to 600 millimicrons. AWratten #61 filter used over the camera will prevent fluorescent lightfrom 'the other ingredients reaching the film orif ortho films are used,an ordinary yellow filter will do. In a copending application by one ofus (Yule) serial number filed concurrently herewith an alternative greenfluorescent material consisting of chrysene recrystallized with 1%naphthacene is described.

One per cent rhodamine G in sandarac resin when illuminated by a mercuryvapor lamp directly (i. e. no filter over the lamp) is excited by the546 and 577 millimicron lines of mercury and fluoresces in the 600 to700 millimicron region of the spectrum. A'Wratten #25 Red Filter on thecamera lens prevents both the light titles of the fluorescentingredients will vary with the types or emulsion usedin the camera,

the transmissions or the filters and the nature Purple (primary blue).

of the printing inks to be used, we have found that the following pointsare satisfactory for creating an original to be reproduced by a processusing commercial inks now in use and with regular panchromatic ororthochromatic emulsions.

Pigment Paint color Fluorescent ingredient taining naphthaccno I 3%Hausa yellow.

Orange red (pri- 17% Toluidinc Toner.

55% Gum sandarac inury rod). cost G (I?) Rhodarn e Anthra ene containingnaphtbacene Light Orangelted 0.5% Hausa yellow. 2.7% Gum sandarac i 1.7%Toluidine Toner. containing Rhoda- 47% Silicon dioxide. mine G (1%). 47%Blane fixe. 1.1% Anthracene connaphtbacene 50% of above magenta aint.51% of above process b 1e paint.

Orange 50% of above yellow paint. I 5)% of above orange red paint.Yellow Greeu 50% of above yellow paint.

7 50% oi above green paint.

Greenish Blue 50% oi above process blue paint.

a 50% of above green paint.

From' the above it will be seen that chrysene is the fluorescentingredient corresponding to hue III in Fig. 2, anthracene plus 1%naphthacene or chrysene with 1% naphthacene is the ingredientcorresponding to hue II, and sandarac containing rhodamine G is the onecorresponding to hue I.

Blane fixe is a commercial barium sulfate (B21604). Chrysene can beprepared as described in Yules copending application mentioned above. Indetermining the proportions of the fluorescent ingredients in the abovepaints, the green was made up first with the maximum possiblefluorescence. This, of course, determines the strength 01' the hue IIand hue III fluorescence required in the other paints. V The (deep)orange-red was then made up relating the hue II to the hue I and fixingthe amount of hue I fluorescence required; exposure times are selectedto make the brightness oi the fluorescent hues efiectively equal.

In each case the solid materials given in the above table are groundto asuitable consistency in an aqueous solution of gum arabic (30% solution)or other suitable vehicle.

Thus we have a palette 0! artists colors having incorporated in each aquantity of fluorescent ingredient (effectively) directly proportionalto one of the subtractive color contents of that one. That is, theamounts of any one of the fluorescent ingredients in the difierentcoloring materials are proportional (not necessarily linearly) to thesubtractive color contents of the materials and inversely proportional(again not necessarily lin early) to the fluorescent emciency of theingredient in those materials. The fluorescent emciency depends on theabsorption by each material of the fiuoro-activating light and ofthefluorescent light. It is not necessary that the amounts or the diflerentingredients bear any special reis made with a non-fluorescent black inkon non-.

fluorescent white base and is then tinted with washes of fluorescentpaints such as those described above. The color separation positives aremade using the light sources and filters above described, but none ofthe printers will have any printing density at the points correspondingto the black lines in the original. The original is then illuminatedwith a light so frared such as incandescent tungsten, the filter ischanged to a. Wratten 88A, and an exposure is made on a high contrastinfrared-sensitive plate. Upon development, this gives a negative or theblack pen lines only with no trace of the colors. A contact positivemade on a high contrast plate such as Kodalith completes the set ofcolor positives to be used in so-called fourcolor reproduction. In thelatter process, highlight screen negatives are made from the colorseparation positives and a line negative is made from the blackpositive. These are printed on metal and etched in the usual manner toproduce a set of printing plates.

In common with the broad process, this special embodiment has thefollowing advantages. Color correction is completely eliminated. Thestep of making separation negatives is also eliminated. A large densityjump can be created between the white background and the lightest colortints because, being non-fluorescent the background density is notincreased by exposure. This results in a positive from which "highlightnegatives are easily made and thus manual opaquing of the highlights onnegatives is unnecessary. Correct color positives for photogravure andcollotype can be made in a single photographic step.

This special embodiment has the additional advantages that the blackpen'lines are eliminated from the color separations automatically. Alsothis process provides that color comics can be properly reproduced by aneconomical photographic process, ireeing the art from the limitations ofthe Ben Day process now used.

Sometimes this special embodiment is a little difiicult to operate ifthe original contains fine black lines because when the threecolors arenot on properly in register with the black, white lines appear. This isdue to the fact that the presence of the black lines in the original,even if underlying the other colors, greatly reduce the fluorescence.This may be overcome by making the black outline drawing first and thenoverlaying this outline with translucent material such as tracing paperand coloring on the translucent material. The black outline drawing andthe overlay are separately photographed. Of course, it is not necessaryto restrict the photographing of the black outline drawing to infraredor any other specific type in this case. Alternatively the black outlinecan be made with a bleachable black ink which is bleached before makingthe color separations.

urce rich in inone material having a What we claim and desire to secureby Letters 'Patent 01 the United States is:

l. The method of producing color separation positives for use in aphotomechanical color printing process which comprises creating anoriginal with coloring materials containingthree fluorescent ingredientsof different fluorescent hues, the ingredients correspondingrespectively to the three subtractive, i. e. yellow, magenta, andblue-green, color contents of the materials, there being at least onematerial having a yellow content, one material having a magenta contentand blue-green content and there being at least two materials having onesubtractive color contentin common and in each pair of coloringmaterials which have a subtractive color content in common, the relativeamounts of the ingredient corresponding to this subtractive colorcontent being proportional to the amounts of this content in the pair ofmaterials and inversely proportional to the fluorescent efliciency ofthat ingredient in those materials, placing three photo-sensitive layerssuccessively in printing relation to'the original, illuminating theoriginal with fluoro-activatin'g light, exposing the layersrespectivelyto fluorescent light only oi said different hues and developing thelayers. 1

2. The method of producing color separation positives for use in aphotomechanical color printing process which comprises creating theoriginal with at least four different coloring materials containingthree fluorescent ingredients,

each one, in all the materials in which it occurs, being in relativeproportion to the amounts of one of the subtractive color contentsrespectively of the hues of the coloring materials, the fluorescent huesof the three ingredients being different and mutually separablespectrally, illuminating the original with fluoro-activating light,exposing three photosensitive layers successively in printing relationto fluorescent light only and respectively or each fluorescent hue onlyfrom the original and developing the layers.

3. The method of producing color separation positives to be used in aphotomechanical color printing process employing three color printersthe original with at least five coloring materials of which blackcontains no fluorescent, ingredient and absorbs infrared and of whichthe others do not absorb infrared and contain three fluorescentingredients of mutually spectrally separable fluorescent hues,corresponding respectively to the three subtractive colors, yellow,-magenta and blue green, the relative amounts of each ingredient in thematerials which contain that ingredient being proportional to the.amounts of the corresponding subtractive color content in thosematerials and inversely proportional to the fluorescent efllciencies orthe ingredients in the materials, placing three photosensitive layerssuccessively in printing relation to the original, illuminating theoriginal with fluoro-activating light, exposing the layers respectivelyto fluorescent light only and of said difierent hues, developing thelayers, placing the fourth photosensitive layer in printing relation tothe original, illuminating the original with infrared light, exposingthe fourth layer to infrared light only from the original, developingthe layer to a negative and making a positive therefrom.

4.'The method of producing color separation positives to be used in aphotomechanical color printing process employing three color printersand one black printer which comprises creating a black outline drawingcorresponding to the portions of an original to be reproduced by theblack printer, overlaying this drawing with translucent o! the originalon color materials the translucent material with containing threefluorescent ingredients of mutually spectrally separable fluorescenthues, there being at least two materials having a subtractive colorcontent in common, the relative amounts of each ingredient in thematerials in which it occurs being proportional 40 to one of thesubtractive color contents of the land one black printer which comprisescreating I hues of the materials and inversely proportional to thefluorescent emciencies of the ingredients in the materials, separatelyphotographing the black outline drawing and making a positive thereofand separately illuminating the overlay with fluoro-activating light,placing three hotosensitive layers successively in printing relation tothe overlay, exposing the layers respectively to fluorescent light onlor said diflerent hues and developing the layers.

ER MURRAY. JOHN A. C. YULE.

material, creating the color portions

